Conventional hydroprocessing units such as distillate, gas oil, and residue hydrotreaters and hydrocrackers preheat hydrogen and oil streams in a series of heat exchangers using reactor effluent as the heating medium. In most cases, the hydrogen and oil streams have been preheated in separate heat exchangers, with downstream control valves employed to properly distribute these single phase streams to multiple passes of a downstream furnace. In other cases, it has been known to premix hydrocarbon and hydrogen to form combined streams which are then passed through heat exchangers. However, these processing schemes require substantial capital investment owing to the need for the multiple heat exchangers and associated piping, valves, and control components. By the same token, maintenance costs are also high.